Field of the Invention
The invention relates to a hearing assistance system comprising an audio signal transmission unit for wireless transmission of a stereo audio signal and at least one ear worn unit comprising a hearing instrument, such as a hearing aid, and a wireless audio signal receiver unit for supplying the hearing instrument with an audio signal received from the transmission unit.
Description of Related Art
Wireless audio signal transmission systems may comprise wireless microphones which are used for transmitting audio signals captured from the voice of a speaker to ear level hearing instruments. For example, wireless microphones may be used by teachers teaching hearing impaired persons in a class room (wherein the audio signal is captured by the wireless microphone of the teacher are transmitted to a plurality of receiver units worn by the hearing persons listening to the teacher) or in cases where several persons are speaking to a hearing impaired person (for example, in a professional meeting, wherein each speaker is provided with a wireless microphone and with the receiver units of the hearing impaired person receiving audio signals from all wireless microphones). Another example is audio tour guiding, wherein the guide uses a wireless microphone.
Another application of wireless audio transmission systems is the case in which the transmission unit is designed as an assistive listening device. In this case, the transmission unit may include a wireless microphone for capturing ambient sound, in particular from a speaker close to the user, and/or a gateway to an external audio device, such as a mobile phone, a TV set or a HiFi system; in this case the transmission unit serves to supply external audio signals to the receiver units worn by the user.
A wireless audio link may be, for example, implemented as an FM (frequency modulation) radio link operating in the 200 MHz frequency band. Examples of analog wireless FM systems, particularly suited for school applications, are described in European Patent Application EP 1 864 320 A1 which corresponds to U.S. Pat. Nos. 7,648,919; 8,158,476; and 8,345,900.
In recent systems the analog FM transmission technology is replaced by employing digital modulation techniques for audio signal transmission, most of them working on other frequency bands than the former 200 MHz band, such as in the 2.4 GHz ISM band.
In general, audio signal receiver units may be integrated within hearing instrument, or they may be provided as a separate device which is connected to the hearing instrument via a standardized electric and mechanic interface (“audio shoe”).
European Patent Application EP 1 531 650 A2 and corresponding U.S. Patent Application Publication US 2005/0100182 A1 relate to a wireless hearing assistance system wherein the transmission unit is designed as an assistive listening device which may transmit a stereo audio signal via a first frequency channel which transmits a first portion of the stereo signal to a first hearing instrument and a second portion of the stereo signal via a second frequency channel to a second hearing instrument.
U.S. Patent Application Publication US 2006/0233385 A1 relates to a binaural hearing aid system wherein the gain setting in each of the two hearing aids is changed depending on whether the other hearing aid is active or not, with the activity to the other hearing aid being checked via a binaural link.
U.S. Pat. No. 9,014,379 B2 relates to a binaural hearing aid system, wherein in each of the two hearing aids the parameter setting of both hearing aids is stored, and wherein the hearing aids are provided with a communication link for exchanging the parameter settings between each other.
International Patent Application Publication WO 2004/110099 A2 relates to a Bluetooth type wireless network, wherein two binaural hearing aids are connected to each other and to external devices, like a mobile phone, via the network.
U.S. Pat. No. 8,565,444 B2 relates to a smartphone which senses the presence of one or two speakers in a headset and a microphone in order to adjust audio output signal of the smartphone according to the stereo or mono capability of the headset connected to the audio output.
International Patent Application Publication WO 2011/146659 A2 and corresponding U.S. Patent Application Publication 2011/0286615 relate to a stereo headset divided into two sub-systems, each one comprising an earpiece; one of the earpieces acts as a master in a network configuration with a Bluetooth type communication device, and the other earpiece acts as a slave, with information received by the master, such as information concerning stereo or mono signal choices, being transmitted to the slave device.
International Patent Application Publication WO 2008/122665 A1 and corresponding U.S. Patent Application Publication 2010/0067723 relate to user interface of a body-worn communication device for communicating with the head-worn listening device; the user interface may be used for manual signal selection and for manual change of hearing aid settings.
International Patent Application Publication 2007/110807 and corresponding U.S. Patent Application Publication 2011/0144779 relate to a headphone for a portable media player, which is capable of detecting the headphone configuration in order to switch from a mono to a stereo signal.